Various devices or features have been used over the years to center and/or flatten a web which is being conveyed. The most common such devices or features are the bowed "Mount Hope" rolls, named for a pioneer supplier of this concept. Another manufacturer provides roll coverings which include spiral grooves having groove sides that are ground at an angle, with opposite leads from the center to the ends. This construction is shown in FIGS. 1 and 2.
The grooved roller of FIG. 1 has a central support 1, or core, that is typically surrounded by a roll cover 2, or outer layer, and that has a plurality of grooves 3 to spread a web. The prior art grooves cause several problems, such as: increased manufacturing costs in milling the roll cover or outer layer, a rough surface that is more likely to tear fragile webs, and grooves that collect dirt from the environment or even pieces of the web itself. FIG. 2 indicates a cross-section of a portion of the roll cover, or outer layer to further illustrate the complexity of the grooves.
In an attempt to prevent damage to light and fragile webs, that manufacturer also supplies multiple-lead finer grooves to attempt web spreading. Other manufacturers weld a solid wire in a spiral configuration around the external surface of a steel roll, with the spiral lead reversed from the center to the opposing ends. Existing rollers with grooves, wires, or other discontinuous surfaces run the risk of damaging or leaving dirt marks on the web.
The manufacture of rolls with such grooves or spiral wire welds requires additional cost and effort when producing the rolls. It has been desired in the field to produce a flat roll or roller that would have the additional effect of preventing wrinkles from forming in a web or of removing wrinkles that form during handling of the web. The present invention provides one such class of devices which achieve the desired performance.